The present invention relates generally to an improved double acting fluid cylinder of tandem chamber construction, wherein a primary chamber is utilized to provide an initial stroke and main motion in the ram directed along a first direction and wherein a tandemly arranged secondary chamber is provided with a resiliently biased and hydraulically dampened secondary piston to buffer, control and temper the rate and extent of motion induced in the ram by the initial stroke and to provide limited secondary reverse motion in an amount proportionally less than the motion of the initial stroke. This action serves to temper the amplitude or ultimate extent of motion induced in the ram in each operational event.
The present invention constitutes an improvement over that certain device and system described and claimed in U.S. Pat. No. 4,481,868, "Fluid Cylinder with Motion Buffered Ram Assembly". In accordance with the present invention, a single spring is utilized to achieve the control of motion in the secondary piston, thus providing a system in which the overall length can be reduced and thus permit installation in smaller spaces and volumes.
Fluid actuated cylinders are utilized for a wide variety of purposes. The operating parameters of cylinders are determined, to a great extent, by the type of operating fluid utilized, the operating pressure and capacity of the source, as well as the manner in which the fluid is controlled while being delivered to the chambers. The cylinder arrangement of the present invention, being tandem, is designed for use preferably with a pulsed pneumatic source in the primary chamber, to achieve quick initial stroke with a partial overdriven or overextended response, and with a hydraulic fluid and a spring or mechanical bias being provided in the secondary chamber, for buffering, modifying and tempering the ultimate response of the overall cylinder to the pulsed input, thus providing an air-hydraulic combination cylinder with desirable operational characteristics.
As indicated, fluid actuated cylinders are utilized for a variety of purposes. The design of the present air-hydraulic combination cylinder makes it particularly adapted for use with devices requiring a rapid initial drive or stroke response to an indicating signal, with the initial drive phase or stroke being slightly overdriven or overextended response followed by a subsequent relaxation phase wherein a portion of the ram motion induced in the initial phase is reversed.
The cylinders of the present invention are particularly adapted for use in controlling and steering high speed webs such as endless abrasive belts or the like which move or travel at high rates of speed in an orbital path along two or more drums which define the orbit. In a typical two drum orbital arrangement for an abrasive belt, one drum drives the belt, with the second or idler drum preferably being used as a "tracking" roll or drum for the system. Because of the high rates of speed normally involved in such orbital webs or belts, highly responsive steering corrections are required in order to control, steer and properly track the web along its orbital path and limit the extent to which the belt will wander or otherwise experience axial run-off.
Most abrasive belt tracking systems employ at least two sensors in order to properly steer the web, one being disposed at each lateral edge of the normal tracking path of the belt. Since the sensors employed normally respond to the occurrence of an abnormal tracking condition, it is normally necessary to oversteer the tracking device to be able to correct the run-out and at the same time properly steer or guide the web along a desired axial path. Because of the high speeds involved, the correctional response or motion must be undertaken rapidly in order to prevent axial run-off of the belt. In order to prevent ultimate over-correction or constant hunting of the system, it has been found desirable to control or steer the web with a correctional cycle which includes two separate phases, the initial phase consisting of an over-adjustment or overly extended rapid drive pulse, i.e., one of excessive magnitude, followed by a relaxation phase which consists of a partial reversal somewhat slower than the initial drive pulse. The over-adjustment occurring in the initial phase is designed to reverse the direction of "wander" of the belt. The relaxation or buffer phase permits partial reversal of the initial over-adjustment with the reversal preferably occurring at a somewhat slower rate than that taking place in the initial phase. In other words, in the initial phase of the correctional cycle, a first over-adjustment pulse is delivered to the cylinder to cause the ram to rapidly move in a first direction, and during the relaxation phase, a partial and relatively slow reversal of motion of the ram occurs. In the air-hydraulic combination cylinder of the present invention, the initial over-adjustment stroke or pulse is obtained by the action of the primary pneumatic chamber, with the primary piston providing the rapid initial response in the ram along a first operational direction. Thereafter, in the relaxation phase a reversal of motion occurs to accommodate and mollify the initial over-adjustment. In a typical belt control application, therefore, the initial over-adjustment is sufficient to immediately correct and reverse the axial travel condition of the belt to prevent run-off, with the relaxation or reversal phase being undertaken to accomplish some residual correction of the axis of travel. In this fashion, control of the web and/or belt is achieved by establishing a new operating datum point for the tracking system each time a belt travel correction event or cycle occurs.
The improved air-hydraulic combination cylinder of the present invention is uniquely adapted for belt tracking control, among other applications where response of the above type is desired, indicated or required. Typically, the improved air-hydraulic cylinders of the present invention include a single housing and ram with tandemly arranged primary and secondary chambers. A double-acting ram is slidably mounted within both chambers of the housing, and primary and secondary piston members are operatively coupled to the ram within the responsive chambers. The primary chamber has a pair of primary fluid ports in communication therewith delivering primary fluid thereto, in this case pneumatic fluid. While steady-state delivery of pneumatic fluid may be utilized in some applications, the device of the present invention is particularly adapted for use with pulses of fluid delivered thereto. Since, the primary fluid ports are typically disposed on opposite sides of the primary piston, double-acting motion of the primary piston and ram may be achieved. The secondary chamber is provided with a pair of secondary fluid ports, with these ports being arranged on opposite sides of the secondary pistons. A fluid conduit directly interconnects the secondary ports, one to another, to hydraulically couple the opposed ends of the secondary chamber together and to permit hydraulic fluid to move therethrough at a controlled rate in response to motion of the secondary piston. The secondary piston is resiliently coupled to the ram through a single compression, so that the ram may move in direct response to the primary piston, and in time-delay response relative to the secondary piston. The motion of the secondary piston relative to the ram is dependent upon forces generated in the spring, with movement of the secondary piston forcing hydraulic fluid through the interconnecting conduit to mutually opposed sides of the piston. Accordingly, the motion of the ram is buffered in both its rate and amplitude, with the buffering action occurring as a result of forces generated in the resilient spring member of the motion buffer assembly interconnecting the ram and the secondary piston and through transfer of hydraulic fluid due to movement of the secondary piston within the secondary chamber.